The circumference of the earth is about 40,000 kilometers. A round trip from CA to Netherlends and back will have electricity going roughly that distance. Speed of electricity times 150 milliseconds is 44,000 kilometers.
That means that the number won't change over time.
Surely, the dominant part of the path city to city is via fiber, so laser light?
That doesn't mean that's were most of the time goes (but ideally it should) - for latency things like light-to-signal, buffers, switching, carrier grade nat, all takes its toll.
Would be interesting to see a detailed breakdown of typical data center(... Cell phone, home broadband user) to same, though. Including every "point" in the path from ram, via cache, pci, network card, routers and switches, media converters and up again... For bonus something like USB keyboard touch to glyph on screen over udp or other low latency protocol...
Delay will in most part be because of distance, forwarding delay in routers are a few 10's of microseconds while switches are at the sub-microsecond level. Stuff like this is quick when they have to handle 100Gbit interfaces.
This also implies that you could materially change that rtt number if you used a faster medium - e.g via air by way of microwave towers.
Which is done for high-speed trading networks: https://arstechnica.com/information-technology/2016/11/priva...